The present invention relates to ligands, various catalyst precursors and catalyst systems derived from these ligands for ethylene oligomerisation to linear alpha olefins in high yield and very high selectivity, and a process for preparing said linear alpha olefins.
Various processes are known for the production of higher linear alpha olefins (for example D. Vogt, Oligomerisation of ethylene to higher xcex1-olefins in Applied Homogeneous Catalysis with Organometallic Compounds Ed. B. Cornils, W. A. Herrmann Vol. 1, Ch. 2.3.1.3, page 245, VCH 1996).
These commercial processes afford either a Poisson or Schulz-Flory oligomer product distribution. In order to obtain a Poisson distribution, no chain termination must take place during oligomerisation. However, in contrast, in a Schulz-Flory process, chain termination does occur and is independent of chain length. The Ni-catalysed ethylene oligomerisation step of the Shell Higher Olefins Process (SHOP) is a typical example of a Schulz-Flory process.
In a Schulz-Flory process, a wide range of oligomers are typically made in which the fraction of each olefin can be determined by calculation on the basis of the so-called K-factor. The K-factor, which is indicative of the relative proportions of the product olefins, is the molar ratio of [Cn+2]/[Cn] calculated from the slope of the graph of log [Cn mol %] versus n, where n is the number of carbon atoms in a particular product olefin. The K-factor is by definition the same for each n. By ligand variation and adjustment of reaction parameters, the K-factor can be adjusted to higher or lower values. In this way, the process can be operated to produce a product slate with an optimised economic benefit. Since demand for the C6-C18 fraction is much higher than for the C greater than 20 fraction, processes are geared to produce the lower carbon number olefins. However, the formation of the higher carbon number olefins is inevitable, and, without further processing, the formation of these products is detrimental to the profitability of the process.
To reduce the negative impact of the higher carbon number olefins and of the low value C4 fraction, additional technology has been developed to reprocess these streams and convert them into more valuable chemicals such as internal C6-C18 olefins. However, this technology is expensive both from an investment and operational point of view and consequently adds additional cost. Therefore it is desirable to keep the production of the higher carbon number olefins to the absolute minimum, i.e. not more than inherently associated with the Schulz-Flory K-factor.
WO-A-98/27124 discloses iron- and cobalt-based ethylene polymerisation catalysts. Said catalysts comprise iron and cobalt complexes of 2,6-pyridinecarboxaldehydebis(imines) and 2,6-diacylpyridinebis(imines) of the formula (I): 
wherein M is Co or Fe; each X is an anion; n is 1, 2, or 3, so that the total number of negative charges on said anion or anions is equal to the oxidation state of a Fe or Co atom present in (I); R1, R2 and R3 are each independently hydrogen, hydrocarbyl, substituted hydrocarbyl, or an inert functional group; R4 and R5 are each independently hydrogen, hydrocarbyl, an inert functional group or substituted hydrocarbyl; R6 is of formula (II); 
R7 is of formula (III); 
R8 and R13 are each independently hydrocarbyl, substituted hydrocarbyl or an inert functional group; R9, R10, R11, R14, R15 and R16 are each independently hydrogen, hydrocarbyl, substituted hydrocarbyl or an inert functional group; R12 and R17 are each independently hydrogen, hydrocarbyl, substituted hydrocarbyl or an inert functional group; and provided that any two of R8, R9, R10, R11, R12, R13, R14, R15, R16 and R17 that are vicinal to one another, taken together may form a ring.
R8 and R13 are each preferably alkyl groups containing from 1 to 6 carbon atoms, and more preferably iso-propyl or tert-butyl groups. R12 and R17 are each preferably alkyl groups containing from 1 to 6 carbon atoms, and more preferably iso-propyl groups.
The polymerisation process of WO-A-98/27124 produces both oligomers and polymers of ethylene. Said products may vary greatly in molecular weight. For example, whilst Example 32 in WO-A-98/27124 illustrates the production of oligomeric olefins, in particular decenes, the majority of the Examples therein produce lower molecular weight polyethylene oils and waxes and higher molecular weight polyethylenes.
Preferred products of WO-A-98/27124 are those with a degree of polymerisation (DP) of about 10 or more, preferably about 40 or more. By xe2x80x9cDPxe2x80x9d is meant the average number of repeat (monomer) units in a polymer molecule.
Thus, on the whole, the catalysts and process of WO-A-98/27124 are particularly directed towards the production of polymers of ethylene.
In WO-A-99/02472, there are disclosed novel iron-based ethylene oligomerisation catalysts that show high activity and high selectivity towards linear alpha olefins. The catalysts are based on iron complexes of a selected 2,6-pyridinedicarboxaldehyde bisimine or a selected 2,6-diacylpyridine bisimine.
In the present invention the term xe2x80x9cbis-(aryliminoalkyl)pyridinexe2x80x9d, or in short, xe2x80x9cbis-aryliminepyridinexe2x80x9d is used to describe both classes of ligands.
In WO-A-99/02472, the oligomer product distribution made with these catalysts is not specified any further, but is implied to be Schulz-Flory in view of the definition, the use, and the determination of the Schulz-Flory K-factor.
In other publications, such as A. M. A. Bennett Chemtech 1999 July, page 24-28; and references mentioned therein, the product composition was stated to obey a Schulz-Flory distribution. The accompanying experimental data in WO-A-99/02472, however, shows that these catalysts afford a product slate with a surprisingly large amount of heavy products.
Further experimenting and analyses have confirmed that the disclosed oligomerisation catalysts afford a product composition which, in comparison with a Schulz-Flory distribution, indeed contains significantly more heavy products than expected.
Table 1 on page 30 of WO-A-99/02472 gives an overview of ethylene oligomerisation experiments catalysed by four different iron complexes (X-XIII). Experiment numbers 16 and 17 of this Table, in which iron complex XI is being used at ethylene pressure of 1.4 MPa (gauge) or 1.5 MPa (15 bar(a)) and 2.8 MPa (gauge) or 2.9 MPa (29 bar(a)) respectively, both give rise to a Schulz-Flory K-factor of 0.79, as derived from the C16/C14 ratio. If it is assumed that a perfect Schulz-Flory distribution is obtained in these experiments, that is to say Cn+2/Cn=K=0.79, it can be calculated that the C30-C100 fraction is 15% wt. and the C20-C28 fraction is 21% wt. on total product. If it is further assumed that the solids mentioned in Table 1 contain the C20-C100 fraction then this should amount to 36% wt. on total product. This should be considered as a maximum solids content since at least the major part of the lowest ethylene oligomers in this fraction remain dissolved in the toluene-solution of the C4-C18 fraction. In Experiment numbers 16 and 17 of Table 1, however, the amount of solids isolated are 14.1 g and 18.0 g, which may be calculated as a solids content of 45% wt. and 58% wt. on total product, respectively.
Similarly for a K-factor of 0.81 it can be calculated that the C20-C28 fraction and the C30-C100 fraction are 22% wt. and 20% wt. on total product, respectively, or maximally 42% wt. for the solids content. For Experiment number 18 in Table 1, also using iron complex XI, but now at pressure of 0 MPa (gauge), i.e. 0.1 MPa (1 bar(a)), the amounts of solids isolated are 2.7 g, which may be calculated as a solids content of 54% wt. on total product.
The distributions obtained in Experiment numbers 16-18 in Table 1 of WO-A-99/02472 clearly indicate that larger quantities of higher carbon number products, i.e. solids ( greater than C20), are produced than would be expected on the basis of the Schulz-Flory K-factor.
The excess of heavy ends has a detrimental effect on the economics of the technology.
In European Patent Application No. 00301036.0, provides a bis-aryliminepyridine MXn complex comprising a non-symmetrical ligand of formula (IV): 
wherein M is a metal atom selected from Fe or Co; n is 2 or 3; X is halide, optionally substituted hydrocarbyl, alkoxide, amide, or hydride; R1-R5, R7-R9 and R12-R14 are each, independently, hydrogen, optionally substituted hydrocarbyl, an inert functional group, or any two of R1-R3, R7-R9 and R12-R14 vicinal to one another taken together may form a ring; R6 is hydrogen, optionally substituted hydrocarbyl, an inert functional group, or taken together with R7 or R4 to form a ring; R10 is hydrogen, optionally substituted hydrocarbyl, an inert functional group, or taken together with R9 or R4 to form a ring; and R11 and R15 are, independently, hydrogen or an inert functional group.
The term xe2x80x9cnon-symmetricalxe2x80x9d is used in relation to the four ortho-positions of the two aryl-imino groups and defines these as such that neither the substitution pattern nor the substituents themselves afford two equally ortho-substituted aryl-imino groups.
A bis-aryliminepyridine ligand of formula (V) is provided, 
wherein R1-R5 and R7-R9 and R12-R14 are each, independently, hydrogen, optionally substituted hydrocarbyl, an inert functional group, or any two of R1-R3, R7-R9 and R12-R14 vicinal to one another taken together may form a ring, and R6, R10, R11 and R15 are identical and are selected from fluorine or chlorine. Futher, a bis-aryliminepyridine MXn complex comprising the ligand of formula (V) and a [bis-aryliminepyridine MYp. Ln+] [NCxe2x88x92]q complex comprising the ligand of formula (V), wherein M is a metal atom selected from Fe and Co, X is halide, optionally subsituted hydrocarbyl, alkoxide, amide, or hydride with n of 2 or 3, Y is a ligand which my insert an olefin, NCxe2x88x92 is a non-coordinating anion, and L is a neutral Lewis donor with n of 0, 1, or 2, are provided. Further, a process for the production of alpha-olefins using one or more such complexes are provided.